The broad objective of this proposal is to understand how stringent amino acid control operates to regulate the expression of an appreciable fraction of E. coli genes. Using a selected ribosomal cistron promoter region, a sizeable degree of definition of promoter characteristics have been possible. It seems that a fairly thorough understanding of the structure and activity of the ribosomal promoter would be needed for further studies on its control. The aim of this proposal is to correlate structure of the DNA of the rRNA with specific characteristics of the transcriptional control of these promoters. Further work will be identification of other factors than ppGpp participating in the control of these promoters and their mode of action. Recombinant plasmids and phages carrying the rRNA promoters fused to easy assayed genes will be used for isolation of both host and rRNA promoter mutants. Studies on the structure of rRNA operons of Mycoplasma will also be performed. The structure and regulation of the RelA gene will be studied for the understanding of cell growth control.